The present invention concerns a commutator device for electric motors, and particularly motors with a rotor comprising one or several coils supplied with electric current by a commutator device.
In a motor of this type, the conducting wires of the coils are connected to corresponding commutator blades mounted around an axle portion of the motor against which the commutator brushes which are connected to leads of a power circuit are pressed. The contact between a contact surface of the brush and the commutator blades is secured by a spring, for instance an elastic arm embedded at one end portion and holding the contact surface close to the other end portion. It is known to lubricate the contact surfaces between the brushes and the commutator on the motor axle in order to reduce wear and lengthen the motor""s life. Conventional motors still undergo wear by electroerosion caused by sparks arising between the brushes and the commutator blades, particularly because of the separation of the contacting surfaces resulting from brush vibrations.
In view of these drawbacks, it is an object of the invention to reduce the wear of the commutator parts of electric motors and enhance the efficiency and reliability of these motors. It is an advantage, furthermore, to provide a commutator device for motors that is compact and economic.
Objects of the invention have been achieved by a commutator device for a motor according to claim 1.
In the present invention a commutator device for an electric motor comprises a housing part and commutator brushes housed in said housing part while each brush comprises a contact surface designed to be pressed against a commutator part of a rotor of an electric motor, and a spring part attached to the contact part so as to exert a force on that contact part in the direction of the rotor""s commutator part, the device further comprising a damping element arranged so as to absorb the vibrations or movements of the contact part of the brushes. The damping of the brushes also allows the life of the motor to be extended, by reducing the sparks arising from instances of separation of the contact surfaces of the brushes from the rotor""s commutator part. The damping element can advantageously comprise a supply of lubricant also serving to lubricate the contact surfaces of the brushes.
The spring part of the brushes can advantageously be an elastic arm extending between a mounting part of the brush that is mounted on the housing part and a contact part that is arranged close to one free end of the brush. The damping element can be arranged along the elastic arm, by enveloping part of the arm. The lubricant supply can be arranged in a reservoir part of the housing part, for instance in the form of a cavity that is arranged around a portion of the spring part of the brushes. The lubricant can be a thixotropic lubricant so that it retains its shape and position in the reservoir while allowing a small amount of the lubricant to migrate along the brushes, for instance by capillarity (surface tension), until it reaches the contact surfaces.
Using a lubricant, both as a damping element and as a lubricant is advantageous in that it allows the design of the commutator device for motors to be simplified and a low-cost device to be realised that still is highly efficient and compact.